Magnetic head assembly formed cooperating head sections bonded together using capillary attraction

ABSTRACT

A magnetic head comprises a gapped media-contact surface formed by a pair of cooperating sections having corresponding planar surfaces abutted to each other. The planar surface of at least one of the sections has at least one narrow elongated slot containing a solidifiable bonding fluid, preferably epoxy, drawn therein under capillary attraction, the fluid upon solidifying bonding the cooperating sections together.

This application is a continuation of application Ser. No. 07/623,848filed Dec. 7, 1990 now abandoned.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

The present invention relates to a magnetic head assembly. Moreparticularly, the invention relates to a method for bonding cooperatingsections of a magnetic head together.

2. Description Of the Relevant Art

A magnetic head used in a magnetic tape recorder or a magnetic diskdrive must meet demanding design specifications necessitated byhigh-density recording formats. Thus, in high density magnetic recorderapparatus, the media-bearing surface of a magnetic head must be durablein order to provide long head life despite high pressure contact overthe head gap area with highly abrasive magnetic tape media such aschromium dioxide tape. Head materials should have compatible wearproperties to prevent head separation loss. Moreover, a magnetic headassembly must have mechanical stability and be able to withstandenvironmental changes (temperature, humidity, shock and vibration)without performance degradation. Furthermore, it is highly desirablethat the head assembly be conducive to a low-cost automated operationfor producing magnetic heads reliably on a mass-production basis.

Various techniques are known in the art for assembling a magnetic headfrom cooperating pole pieces. U.S. Pat. Nos. 3,909,932 and 4,901,179 areexemplary wherein gap-forming pole pieces are aligned facing each otherwith a bonding material, such as glass, at the apex of a V-shaped grooveextending beneath the gap region.

It is also known in the art to position pole pieces a fixed distanceapart and draw bonding glass into the space therebetween by capillaryaction to form the gap. See for example U.S. Pat. Nos. 3,246,383;3,751,803; and 3,824,685.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide a method of assembling a magnetic head from first and secondsections that is of low cost and is readily suitable to a high-volumemass-production assembly operation.

In a presently preferred embodiment, the method comprises the steps of(i) forming from either section, or both sections, at a joint interfacetherebetween, a relatively narrow capillary slot and a fluid-receivingtrough in intersecting relationship with the capillary slot, (ii)supplying a solidifiable bonding liquid into the trough while heatingthe first and second sections to a temperature in a bonding temperaturerange to cause the liquid supplied to be drawn from the trough into thecapillary slot under capillary attraction, and (iii) curing the liquidto form a solid which bonds said first and second sections together bymeans of the solidifiable liquid in the trough and the solidifiableliquid drawn into the capillary slot.

Also, a new and improved magnetic head, manufactured by the methodaccording to the invention, is provided. The magnetic head comprises agapped media-contact surface formed by a pair of cooperating sectionshaving corresponding planar surfaces abutted to each other,characterized by the planar surface of at least one of the sectionshaving at least one narrow elongated slot containing a solidifiablebonding fluid drawn therein under capillary attraction, the fluid uponsolidifying bonding the cooperating sections together.

A particular advantage of a magnetic head having bonded half sections inaccordance with the present invention is that it is readily suited to ahigh-volume mass production operation. This is because bonding materialneeds to be deposited into only one end of the fluid-receiving trough.Each elongated slot, by virtue of its intersecting relationship with thefluid-receiving trough, is filled automatically by drawing bondingmaterial from the trough under the influence of capillary attraction.Thus, for each magnetic head, bonding material deposited at one pointserves to fill the fluid-receiving trough and each capillary slot,thereby bonding (and reinforcing) the two half sections of the headassembly together in each of two orthogonal directions.

A further advantage of the present invention is that multiple magneticheads can be bonded simultaneously. That is, by temporarily couplingcorresponding half sections of multiple heads together along a commoninterface, a single fluid-receiving trough can serve for supplyingbonding material to all head assemblies at the same time.

These advantages, as well as other advantages, will become more apparentin the detailed description of a preferred embodiment presented below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein:

FIG. 1 is a perspective view of a magnetic head assembly in accordancewith the invention;

FIG. 2 is a plan view of the media-contact surface of the head of FIG.1; and

FIGS. 3 through 13 illustrate process steps involved in the manufactureof the magnetic head.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows generally a magnetic head 10, manufactured in accordancewith the present invention, comprised of a relatively thin magnetic core12 sandwiched between two non-magnetic substrates 14. The head 10 isassembled generally from four quarter sections, denoted 16, 18, 20, 22.These four quarter sections are bonded together in two separate steps.The first bonding step, which is conventional, bonds two quartersections together to form a half section; the second bonding step, whichis in accordance with the teachings of the present invention, bonds twohalf sections together to form the magnetic head 10.

Prior to the first bonding step, poles 23, 24, on opposite sides of agap 25 of the core 12, are sputter deposited, by means well known in theart. Preferably, a pole of full width is deposited on two of fourquarter sections. Alternatively, a pole of half width can be depositedon all four quarter sections, and corresponding quarter sections arebonded together (pole to pole) to form a pole of full width.

Each pole of the core 12 may comprise a single film of magnetic materialor, preferably for high frequency recording, may be a laminatedstructure comprised of thin layers of magnetic material alternating witheven thinner layers of a dielectric material. The magnetic material canbe, for example, FeRuGaSi, whereas the dielectric can be SiO₂, Zr oxide,or the like.

The first bonding operation serves to form the two halves of themagnetic head 10 that lie on opposite sides of the gap 25. For thatpurpose, each of the two quarter sections having a pole of full widthdeposited thereon is bonded, respectively, to one of the other twoquarter sections, with the pole sandwiched between the two quartersections bonded. In this conventional bonding operation, an epoxy iscoated directly on one or both of the surfaces to be bonded, preferablyby means of a so-called oil dipper tool.

The second bonding operation, which is the essence of the presentinvention, serves to bond the two half sections of the magnetic head 10together, thereby forming the composite head structure of FIG. 1. As isexplained in detail hereinbelow, this second bonding operation isachieved by clamping corresponding planar surfaces of each half sectiontogether in abutting engagement, then heating the two halves to abonding temperature while drawing a solidifiable bonding fluid,preferably epoxy, between the two planar surfaces under the influence ofcapillary attraction. The fluid drawn between the two half sectionssolidifies and thereby bonds the two half sections together. FIG. 2,which is a plan view of the gapped media-contact surface of the magnetichead 10, illustrates the two bonding planes.

In practicing the presently preferred method of the invention, epoxy isdrawn between the two half sections by means of an elongated capillaryslot 26 (FIG. 2) cut from each non-magnetic substrate 14 of theaforementioned planar surface of one of the half sections of themagnetic head 10. Each slot 26 extends the full depth of the halfsection and, as shown, the two slots 26 are located on opposite sides ofthe core 12. Epoxy is supplied to each capillary slot 26 by means ofdepositing epoxy into a fluid-receiving trough 27 (FIG. 1) cut from thecorresponding planar surface of the other half section of the magnetichead 10. The trough 27 is orthogonal to the core 12 and extends acrossthe full width of the half section. The trough 27 thereby cuts acrosseach capillary slot 26 when the respective planar surfaces of the twohalf sections of the magnetic head 10 abuttingly engage each other.

The trough 27 is filled with epoxy which bonds the two half sectionstogether at their common interface orthogonal to the core 12. Bothelongated slots 26 are also filled with epoxy when epoxy is drawn fromthe trough 27 under the influence of capillary attraction. The epoxy inthe slots 26 serves to further bond the two half sections together, onboth sides of the core 12, orthogonal to the bond along the trough 27.

FIGS. 3 through 13 illustrate more clearly the fabrication and assemblyprocess for the magnetic head 10. FIG. 3 is a plan view of a wafer 30which is made of a material suitable for the aforementioned non-magneticsubstrate 14. For that purpose, I selected MnNi oxide because of itsexcellent wear-resistant property. Furthermore, MnNi oxide and the corematerial (FeRuGaSi and/or a dielectric such as Zr oxide) have respectivethermal expansion coefficients that are well matched over a temperaturerange of 20° C. to 800° C. FIG. 3 shows orthogonal X-Y dicing lanes 32,34 cut from the wafer 30. The lanes serve for subsequently dicing thewafer 30 into a plurality of head quarter sections, denoted 35.

FIG. 4, which is an enlarged cross-sectional view of the wafer 30 alongthe lines 4--4 of FIG. 3, shows that the wafer 30 is first broken alongthe dicing lanes 32 (by means of a parting tool) into columnar strips 36of quarter sections 35.

FIG. 5 shows that each quarter section 35 of each columnar strip 36 isthen sputter deposited with a magnetic material which serves as one ofthe poles of the core 12 of the magnetic head 10. Preferably, the core12 comprises a multilayer structure having alternating layers of themagnetic material FeRuGaSi and the dielectric Zr oxide. Each magneticlayer and each dielectric layer are sputter deposited, by means wellknown in the art, to a thickness of 2 μm and 100 nm, respectively.Typically, each laminated pole includes a total of ten layers ofmagnetic material, to form essentially a 20μ thick multilayer.

The deposited core 12 of each quarter section 35 is bonded to the bottomsurface of the corresponding quarter section of the adjacent columnarstrip (FIG. 6). Preferably, this is done, as described previously, byfirst applying a liquid epoxy by means of an oil dipping tool to thecore 12 and the bottom surface of each quarter section 35. Each strip 36is then rotated ninety degrees (90°) sideways, and columnar strips arethen clamped together (by means not shown) until the epoxy solidifies,thereby bonding corresponding quarter sections of adjacent stripstogether. Each pair of bonded quarter sections forms a half section, asdescribed in detail hereinbelow.

FIG. 7 shows that the bonded columnar strips 36 are then ground to aflat finish on their top and bottom surfaces, as viewed in the drawing.

FIG. 8, which is a plan view, shows that the bonded columnar strips 36are sliced, perpendicular to the plane of each core 12, into rows. Thebest alignment of opposing pole pieces occurs when a half section fromone row is bonded to the corresponding half section of the adjacent row.Accordingly, it is preferred that adjacent rows, denoted A-1, A-2; B-1,B-2; C-1, C-2, etc., are paired.

FIG. 9, which is a partial perspective view, shows that theaforementioned fluid-receiving trough 27 is cut from the upwardly facingplanar surface 45 of every second row of bonded half sections. As shown,each trough 27 is cut along an entire row, orthogonal to each core 12 inthat row. In addition, a groove 47 is cut from the same set of alternaterows parallel with the respective trough 27. Each groove 47 (also shownin FIG. 1) serves as a window for a head coil.

FIG. 9 also shows that the aforementioned capillary slots 26 are cutfrom the upwardly facing planar surface 45 of the alternate rows ofbonded half sections. To that end, a pair of spaced capillary slots 26is cut for each core 12, with each core being parallel with and midwaybetween a corresponding pair of slots 26. Thus, each capillary slot 26in one row of bonded half sections is orthogonal to and co-planar withthe fluid-receiving trough 27 cut from the adjacent row of halfsections.

FIG. 9 also illustrates that a right-angled shoulder 49 is cut fromopposing edges of each row of bonded half sections, co-planar with andparallel to each trough 27. Each shoulder 49, which is cut with a finegrit dicing blade, serves advantageously for aligning opposing polesacross the gap 25 when two half sections of a magnetic head 10 arebonded together.

FIG. 10 is a plan view of a portion of the row A-2 of bonded halfsections with its capillary slots 26 facing downwardly. As shown, twoslots 26 are cut from the planar surface 45 of each bonded half section,parallel with and on opposing sides of each core 12. In a presentlypreferred embodiment, each slot 26 is approximately one (1) mil wideand, after surface lapping, is approximately three (3) mils deep.

FIG. 10 also shows a bonding notch 50 cut in the plane of the core 12from the surface of each bonded half section opposite the capillaryslots 26. As shown, the notch 50 is somewhat wider than the plane of thecore 12. (A similar notch 50 is cut from all rows of bonded halfsections.) The notch 50 is filled with epoxy at this time. This epoxyfunctions to provide added structural support to each bonded halfsection on each side of the core 12.

FIG. 11 shows corresponding half sections of a portion of rows A-1 andA-2 oriented prior to bonding to each other. In the actual bondingposition, the row A-1 of bonded half sections is clamped (by means notshown) to the row A-2 of half sections so that relatively constantpressure is applied to their corresponding planar surfaces 45 when theyabuttingly engage each other. At the joint interface formed by the twoplanar surfaces, the fluid-receiving trough 27 lies in intersectingrelationship with the capillary slots 26, and the cores 12 of the rowA-1 are aligned with corresponding cores of the row A-2. The alignmentof the respective cores is facilitated by means of the right-angledshoulders 49 cut from the top and bottom corners of the planar surfaces45.

Actual bonding is accomplished by first heating the bonded half sectionsto a temperature in a bonding temperature range. In a presentlypreferred embodiment, the MnNi oxide is heated to a temperature ofapproximately 75° C. With the non-magnetic substrate heated, liquidepoxy is supplied by means of the aforementioned oil dipper tool, to oneend of the fluid-receiving trough 27. The heated substrate helps tolower the viscosity of the epoxy and to thereby draw the epoxy along theentire length of the V-shaped trough 27. As the epoxy flows, it is drawnup into each slot 26 under capillary attraction, thereby filling eachslot.

The bonded half sections are then heated to an elevated temperature ofapproximately 120° C. As the epoxy is heated, it hardens thereby bondingcorresponding half sections to each other.

I have found that the trough 27 fills with epoxy as epoxy is drawn intoeach slot 26 under capillary action. Only a small amount of epoxyactually leaves each slot 26 and enters the coil aperture 47 which, ofcourse, also lies in intersecting relationship with each capillary slot.If the capillary slots are too large, however, epoxy flows toovigorously and fills the coil aperture. With each capillary slotapproximately 1 mil wide and 3 mils deep, spillage into the aperture 47has not been a problem. As shown, the epoxy that does enter the aperture47 merely collects at aperture corners common to the plane of slot 26.Thus, it is not necessary to initially cut a coil aperture that isoversized. This is an important consideration because, for a fixedpermeability, a small coil aperture perimeter increases head efficiencyand minimizes inductance.

FIG. 12 shows corresponding half sections bonded together with theirrespective top surfaces ground to a final height.

FIG. 13 shows that the bonded half sections are then cut and ground to adesired final thickness. In doing so, the magnetic head 10 is chosen tohave a desired final configuration of approximately 2 mm by 2 mm outerdimension for its major surface; the media-contact surface is lapped toform a gap depth of 25 μm which provides an estimated head life of 2500hours.

In a presently preferred embodiment, epoxy type 410-7, purchased fromthe Ablestick Company of Gardena, Calif., is utilized. This epoxy isparticularly advantageous because in filtered form (impurities removed),a bonding line of a width less than 0.26 micron can be formed.

It will be understood by those skilled in the art that other fluidbonding materials, such as glass, can be utilized in accordance with theteachings of the present invention. If glass were to be used, afterliquefied glass is drawn by capillary action into the slots 26, the coresections of the magnetic head assembly would be cooled to change theglass from a liquid state to a solid.

The invention has been described in detail with reference to thefigures; however, it will be appreciated that variations andmodifications are possible within the spirit and scope of the invention.For example, I have shown that "capillary attraction" is particularlyadvantageous in the manufacture of a composite head having a gapped coresandwiched between non-magnetic substrates. It will be understood bythose skilled in the art, however, that capillary attraction, inaccordance with the teachings of this invention, is also suitable forbonding half sections together comprised essentially of magneticmaterial.

It will also be understood by those skilled in the art that capillaryslots 26 can be cut from the planar surface 45 of both half sections tobe bonded together. When slots 26 are cut from both half sections,corresponding slots from bonded half sections can be aligned or offsetfrom each other. If, on the other hand, capillary slots 26 are cut fromonly one half section, as is the case with the preferred embodimentdescribed herein, such slots may be cut from the half section from whichthe fluid-receiving trough 27 is formed.

What is claimed is:
 1. A gapped magnetic head comprising a first headsection and a second head section abutted against each other at a commoninterface, said magnetic head further comprising:(a) two non-magneticsubstrates in each of said sections; and (b) magnetic cores sandwichedbetween each pair of said non-magnetic substrates, wherein said firsthead section includes at least one narrow elongated slot extendingtherethrough, positioned on one side but not in contact with saidmagnetic core and parallel to and contiguous with said common interface,for receiving a solidifiable bonding fluid drawn therein under capillaryaction, the fluid, upon solidifying, forming a column of solid bondingmaterial which bonds said head sections together.
 2. A gapped magnetichead as defined in claim 1 in which said bonding material is epoxy.
 3. Agapped magnetic head as defined in claim 1 in which said second sectionincludes at least one narrow elongated slot extending therethrough,positioned on one side but not in contact with said magnetic core andparallel to and contiguous with said common interface, for receiving asolidifiable bonding fluid drawn therein under capillary action, thefluid, upon solidifying, forming a column of solid bonding materialwhich bonds said head sections together.
 4. A gapped magnetic head asset forth in claim 1 further characterized in that said magnetic coresare aligned with each other when said head sections are abutted at saidcommon interface, with said gapped magnetic head further including amagnetic transducing gap extending between the aligned magnetic cores.5. A gapped magnetic head as set forth in claim 4 further characterizedin that said aligned magnetic cores are in direct contact with oneanother after the had sections are bonded together.
 6. A gapped magnetichead as defined in claim 4 further characterized in that the magnetictransducing gap is of insufficient size to allow a solidifiable bondingfluid to flow between said head sections.
 7. A gapped magnetic headhaving a magnetic transducing gap, said head comprising:(a) a first headsection comprised of a magnetic core sandwiched between a pair ofnon-magnetic substrates; (b) a second head section comprised of amagnetic core sandwiched between a pair of non-magnetic substrates andabuttingly engaging said first head section wherein a common interfaceis established therebetween; and (c) each non-magnetic substrate of atleast one of said head sections having a relatively narrow elongatedcolumn of solid bonding material which is not in contact with saidmagnetic core, said column being contiguous to said common interface andparallel with aid sandwiched core, said column being fabricated byfilling a relatively narrow elongated slot in each non-magneticsubstrate of said head section with bonding material introduced thereinvia capillary action.
 8. A gapped magnetic head as defined in claim 7 inwhich said bonding material is epoxy.
 9. A gapped magnetic head as setforth in claim 7 further characterized in that said magnetic core ofsaid first had section is aligned with said magnetic core of said secondhead section with said magnetic transducing gap extending between saidmagnetic cores.
 10. A gapped magnetic head as set forth in claim 9further characterized in that the aligned magnetic cores are in directcontact with one another after the head sections are bonded together.11. A gapped magnetic head as defined in claim 9 further characterizedin hat the magnetic transducing gap is of insufficient size to allow asolidifiable bonding fluid to flow between said head sections.
 12. Agapped magnetic head as set forth in claim 7 wherein said first headsection further comprises a rod of solid bonding material at the commoninterface, said rod being remotely located from said gap and extendingthrough its sandwiched core to the other substrate and fabricated byfilling with bonding material an open ended fluid receiving trough insaid first head section.
 13. A gapped magnetic head as set forth inclaim 12 wherein said column extends in intersecting relationship withsaid rod.
 14. A gapped magnetic head comprising a first said section anda second head section abutted against each other at a common interface,said magnetic head further comprising:(a) two non-magnetic substrates ineach of said sections; and (b) magnetic cores sandwiched between eachpair of said non-magnetic substrates, wherein said first head sectionincludes at least one elongated column of solid bonding materialextending through said first head section positioned on one side but notin contact with said magnetic core and parallel to and contiguous withsaid common interface, formed from a solidifiable bonding fluid drawnunder capillary action into at least one narrow elongated slot includedin aid first head section, the fluid upon solidifying bonding said headsections to each other.